1. Field Of The Invention
The present invention relates to an ultrasonic cutter and, more particularly, to an ultrasonic cutter suitable for cutting the fixation materials used in forming orthopedic cast type dressings for immobilizing the affected body parts of orthopedic patients.
2. Prior Art
Both plaster of Paris bandages which use plaster as a curing agent and synthetic cast bandages which use a synthetic resin as a curing agent are known fixation type materials used for the fixation, support, protection or correction of orthopedic injuries such as fractures, dislocations, sprains, deformities and so forth. Such fixation materials are formed in such a manner that, on an affected or injured body part, an under-wrap, which is usually a cotton bandage or a tubular bandage composed of cotton, polyester and so forth, is first wound or applied onto the affected body part and a plaster of Paris bandage or a synthetic cast bandage is then wound and hardened onto the under-wrap.
Such a fixation material needs to be partially or wholly cut off at some point in time during the treatment of the affected body part or when the affected part is cured. As the cutters used for cutting such fixation or cast type materials, there are known power cutters, wire type cutters, heated blade type cutters, and ultrasonic cutters. Of these known cutters, the power cutters, wire type cutters, and heated blade type cutters each have several drawbacks, whereas the ultrasonic cutter, which is constructed so as to cut the fixation material by use of a cutting edge vibrated by an ultrasonic vibrator, is small in size and light in weight; it makes no noise nor does it produce a harmful gas; and it gives no sensation of fear to the patient. Furthermore, the ultrasonic cutter can easily cut through either a plaster of Paris bandage or a synthetic cast bandage. Thus, the ultrasonic cutter is preferred.
However, the ultrasonic cutter has a very large cutting force so that there is the danger that if, during operation, the blade happens to touch the skin of the patient, however slight the touch may be, the skin of the patient may be heavily wounded. Thus, a preventive measure against such a danger must be taken. There have so far been proposed several methods wherein, according to each, the electrostatic capacity between the cutting blade and the skin is used as a factor for determining the oscillation frequency of an oscillator so that the vibration of the cutter is controlled by utilizing the variation caused in the oscillation frequency of the oscillator when the cutting blade comes close to the skin. See Japanese Unexamined Patent Application Publication Nos. Sho 61-22857, Sho 61-22858, Sho 61-22859. However, in this case, differences in the controlled vibration occur in accordance with the individual differences among patients and the kinds and states of the under-wrap used. Thus, a high reliability cannot always be obtained.
Moreover, a further method has been proposed by the present applicant, according to which a blade cover is provided so as to surround the cutting blade, the blade cover being displaceable in the longitudinal direction of the cutting blade so that the length of the cutting blade which projects from the blade cover is adjustable. In this situation, the fixation material is cut by the cutting blade with the leading end of the blade cover kept in contact with the surface of the fixation material thereby preventing the cutting blade from coming into contact with the skin. In this case, several drawbacks likewise exist. For example, it is difficult to adjust the exposed length of the cutting blade since the distance between the rear surface of the fixation material and the skin is not always constant. Also, since the cutting edge is formed extending as far as the leading end of the cutting blade, the cutting edge is apt to catch the under-wrap lying inside of the fixation material and thus, unless cutting even the under-wrap, the cutter blade cannot be moved forward anymore. As a result, since the bandage constructed with the under-wrap is of such a nature as to be hardly cut by the ultrasonic cutter, the cutting of the fixation material cannot be smoothly performed. In addition, since the cutting blade is surrounded by the blade cover, the operator cannot look straight at the cutting edge even if the blade cover is made of a transparent material. The handling of this type of cutter is not easy.